Operations to drill into the earth's crust, such as to explore for and/or to extract petroleum and the like, usually employ lengthy rotary drill strings. A drill string typically includes a series of interconnected pipes with a drill bit disposed upon one end. The drill string usually is substantially vertically oriented, or frequently is angled to drill an inclined hole, with drilling progressing downward into the earth from the ground's surface. Instances where drilling is generally downward, in concert with the forces of gravity, commonly are referred to as "down hole" operations. Improved technologies and continuing demand for petroleum and other subsurface mineral resources have made it possible also to economically engage in "up hole" drilling. In up hole operations, drilling commences upon a mountainside and proceeds upward against the force of gravity, with the drill string inclined, permitting the hole to be cut at an upward angle.
As drilling progresses, a cylindrical subsurface core sample is produced and may be retained in an inner tube or "core barrel" disposed coaxially within the hollow drill string interior. An important aspect of core drilling is the periodic retrieval of the core sample from the hole for analysis. Retrieval of the sample is performed using a variety of core barrel assemblies. A succinct and helpful background explanation of core drilling and core sample retrieval processes may be had by reference to U.S. Pat. No. 4,466,497 to Soinski, et al. The present invention, while adaptable for use in other core barrel assemblies, is particularly intended for use in conjunction with a wire line core barrel apparatus similar to that disclosed in U.S. Pat. No. 4,466,497, which is hereby incorporated by reference.
To safely retrieve an intact core sample from a drill hole, the core barrel must be properly located and securely maintained in place during drilling. In practice, a latch assembly is used to properly locate the core barrel with respect to the drill bit and lock the core barrel in place in the string. Commonly, a landing ring is fixed at a predetermined location upon the inside wall of the drill string at a specified distance above the bit, to indicate the proper location for the core barrel. A latch assembly is specially connected to the top of the core barrel. The latch assembly and core barrel are placed in the drill string. When the core barrel has been lowered to the proper location in a down hole, or has been hydraulically pumped up to the proper place in an up hole, the latch assembly contacts the landing ring, preventing the entire core barrel assembly from proceeding any further through the string.
It is essential, for personnel safety reasons as well as for efficient and economic core drilling and core sample retrieval, that the core barrel be held stationary (with respect to the drill string and bit) during drilling. To this end, the latch assembly includes elements to securely but releasably attach the locking assembly to the inside wall of the drill string immediately before, and during, drilling. Yet the ideal latch assembly is easily deliberately disengaged during drilling interruptions to allow the core sample to be retrieved to the earth's surface. U.S. Pat. No. 4,466,497 teaches an apparatus for accomplishing these foregoing objects.
However, because the latching process occurs out of sight, hundreds or thousands of feet up or down a hole, it can be difficult for drilling crews using known devices to determine if and when the latch assembly has contacted the landing ring and is securely locked to the drill string prior to commencing drilling. Perhaps even more importantly, it is also difficult for the crew to receive notice of instances when the latch assembly has become disengaged--often by popping slightly upward within a down hole, or slipping slightly down an "up hole"--from the drill string during drilling. Detachment of the latch assembly from the drill string, for any reason, while drilling is in progress can result in serious damage to the drilling equipment and/or destruction of the core sample, resulting in the loss of valuable time, subsurface geological data, and machinery. More critically, unanticipated or unnoticed disengagement of the latch assembly during drilling can pose a genuine risk of life-threatening injury to drill crew personnel, particularly to crews working on "up hole" rigs.
It is known in the art to provide elements upon a latch assembly which cause brief pressure fluctuations in the drill string for the purpose of notifying the rig crew when the latch assembly has landed. Unfortunately, prior devices send signals that are comparatively fleeting and can easily go unnoticed by the crew. Also, prior art devices may send false positive signals whenever the latch assembly becomes snagged or caught, however temporarily, in the drill string prior to landing on the landing ring.
Thus, there is a need for an apparatus that reliably indicates to a drill crew when the latch assembly has properly bottomed out and is locked in place within the string. A need also remains for such an indicating apparatus that encourages an affirmative conduct from the crew in response to the indication. Also, a need remains for an apparatus which automatically warns the crew when inadvertent disengagement has occurred. Such an apparatus preferably should be simple, affordably manufactured to encourage use, and extremely rugged to tolerate down hole conditions, elevated pressures, and rough handling in the field. Against this background, the following invention was developed.